Neutron fluence distribution by bone and hair

In the criticality accident in Tokai-mura on 30 September 1999, two workers received especially high dose of neutrons and GAMMA-rays over their bodies. We measured the activities of neutron-induced BETA-emitters in the hair and bone of the workers to estimate the distribution of neutron fluence in the whole body. The measurement of 32P in hair samples taken from the head and pubis shows that both workers received higher doses of irradiation to the frontal side of their trunks than to the head. For a more detailed mapping of neutron fluence in the body, the measurements of 32P and 45Ca in bone were very effective. The results of bone analyses show that one worker (worker A) received a higher dose of neutrons at the frontal right side of the trunk, and that the dose decreased with the distance from the central part of the body. The other (worker B), seems to have gotten a higher dose of irradiation in the face, hands and waist. The 45Ca concentration ratio of worker B to worker A in the iliac bone agrees not only with the 32P concentration ratio in the pubic hair, but also with the ratio of the estimated average doses for the whole body from lymphocyte number, chromosome abbreviation and 24Na activity in the blood. This suggests that the dose to the abdomen could contribute mainly to the estimation of the average dose from the parameters in the blood. The analyses of BETA-emitters in hair and bone gave us valuable information for the estimation of the dose received by particular organs, which are critical for the health conditions of the workers